1. Field of the Invention
The present invention relates to an illumination optical system and a fluorescent microscope.
2. Description of the Related Art
Critical illumination and Koehler illumination are well known as typical illuminating method.
The critical illumination is an illuminating method for forming a light source image on a sample. Although bright illumination can be realized in the critical illumination, the distribution of luminance on a sample depends on the luminance distribution for the physical expansion of a light source (hereinafter referred to as the “luminance distribution” of a light source). To be more practical, the luminance distribution of a light source image depending on the luminance distribution of a light source and a projection magnification can be the luminance distribution on a sample as is. Therefore, it is hard to uniformly illuminate the sample.
On the other hand, the Koehler illumination is an illuminating method for forming a light source image at the position of the pupil of an objective in the illumination of, for example, a fluorescent microscope etc., and forming an image of a field stop on a sample. The luminance obtained by the Koehler illumination is inferior to the luminance by the critical illumination. However, since the luminance distribution on the sample does not depend on the luminance distribution of a light source, the sample can be illuminated more uniformly.
Thus, there is trade-off between the uniformity in illumination and the luminance. However, since the uniformity in illumination is generally more important in illuminating a microscope, the Koehler illumination is widely used for the illumination of a microscope.
As the technology for further improving the uniformity in illumination in the Koehler illumination, the Japanese Laid-open Patent Publication No. 2005-283879 and the Japanese Laid-open Patent Publication No. 2004-004169 have been disclosed. In the Koehler illumination, although the unevenness in illumination depending on the luminance distribution of a light source can be suppressed, the unevenness in illumination depending on the characteristic (hereinafter referred to as a “light distribution characteristic”) of different luminance for each angle with respect to a light source cannot be suppressed. In the technology of the Japanese Laid-open Patent Publication No. 2005-283879 and the Japanese Laid-open Patent Publication No. 2004-004169, the unevenness in illumination depending on the light distribution characteristic of a light source can be suppressed by forming a plurality of light source images using a fly eye lens. Thus, a sample can be furthermore uniformly illuminated.
Incidentally, the illuminating state requested to an illumination optical system for a microscope is not constantly determined. That is, the uniformity in illumination can be the most important. And the other times, the luminance can be improved at the cost of the uniformity in illumination. Thus, the illumination optical system for a microscope is requested to have the function of adjusting the balance between the uniformity and the luminance in illumination in addition to the basic uniformity of illumination.